Students take part in a demonstration to protest over higher tuition fees in London, England. Photograph: Scott Barbour/Getty Images

Aaron Porter, 25, has just moved back in with his parents in Norbury, south London, after graduating in English literature from the University of Leicester. Not quite the profile you might expect of a man who, as the new president of the National Union of Students, is about to lead one of the fiercest political battles in a generation.

Porter has only months in this new age of austerity to convince Lord Browne, who is carrying out a major review into university financing, that the government should not raise the cap on student fees.

If he fails, hundreds of thousands of young people he represents now – and millions in the future – will face an increasingly US-style market in higher education. That could mean starting their working lives with debts of £50,000 or more. "I've got a hell of a lot on my plate," he admits.

The campaigning begins in earnest tomorrow, when thousands of students and lecturers team up for 70 events across the country, hoping that higher education will be spared the worst of the cuts to be unveiled in Tuesday's emergency budget.

Porter might be living with his parents – a policeman who grew up in London and a teacher from Trinidad – but by day his job is as high-powered as they come. Dressed in a smart dark suit, striped shirt, red tie and shiny black shoes, he is due to go from this interview with the Observer to a one-on-one meeting with Lord Browne. From there it is on to an advisory forum with top figures in the field including Professor Steve Smith, president of Universities UK, which represents all vice-chancellors.

Porter officially becomes NUS president on 1 July, but he has already met Vince Cable, secretary of state for business, innovation and skills, and tomorrow he will sit down with David Willetts, the universities minister. In between the occasional dinner cooked by his mother, he is working 10 to 20 hours a day, seven days a week. "The stakes are so high – it is imperative I get my point across," he says.

Success, says Porter, is "ensuring that a market in fees does not emerge". And failure? "The disaster would be a real market in fees coupled with cuts from the government... it will devastate some people's lives." He is fighting hard to stop universities getting their way and lifting the £3,225-a-year cap on fees (due to rise to £3,290 this year).

Porter is already worried about predictions that this summer 150,000 pupils who have the ability to go to university will never make it. Tackling that issue is what he sees as his key role: "It is vital – I have to stand up to defend what could be a lost generation of young people. And also ensure that education can continue to be based on ability, and not ability to pay. That is the real battle we are up against."

It is a battle for which the NUS has created a new strategy. One of the youngest unions in the country has given up shouting from the sidelines and decided instead to step into the fray.

"We've moved from irrelevance to the centre of the debate," he says. "By ensuring we have evidence-based policy and engaging in the debate that is happening, not in some imaginary one." Porter remembers 2004, when he was 19 and the decision was being taken to increase fees from their original level of £1,000 a year. At that time the NUS stuck to a position opposing all tuition fees, calling instead for the reinstatement of grants.

But, he argues, the argument had already been lost and the time had come to move on. "There came a point when the debate was no longer 'should there be fees or not?', but 'how do we fund higher education?' Rather than sitting at the table, we were standing outside shouting. We weren't taken seriously: we were left out in the cold."

It was his predecessor, Wes Streeting, who fought to change the NUS from the inside, dropping its opposition to contributions from students. Instead, the organisation came up with an alternative – a graduate tax, which would see students face a slightly increased rate of income tax over their careers. It was a fight to get the union to accept it and now Porter is determined to maintain the policy. "There are some that think we should stick to the principled position of free education. But if vice-chancellors expect us to stand on the outside waving placards they are sorely mistaken."

Porter is a member of the Labour party but decided to run for the role of president as an independent, believing that would be the best way to serve students. Student support for Labour has ebbed away in recent years. A poll carried out before the general election suggested 50% of students were planning to vote for the Liberal Democrats.

Porter believes Nick Clegg's party has placed itself in a difficult position. After all, it promised in its manifesto to phase out fees – a hugely popular move. Yet in the coalition agreement the party agreed to await the outcome of Browne's review. Should it be unpalatable to the party, Clegg and his negotiating team agreed that Lib Dem MPs would abstain, allowing the review's conclusions to be implemented if supported by the Conservatives and Labour. Porter knows that the party – and especially Cable – is under from pressure from vice-chancellors who insist fees must go up if they are to compete successfully with foreign competitors. The universities believes fees should be seen as an additional income on top of government funding – not an alternative.

"There are tens of thousands of students who voted for the Liberal Democrats on a pledge that they would not raise fees," says Porter. "It they do not stick to that position they will not only lose the trust of students but the general public. I think it would be political suicide for the Lib Dems to go into coalition with the Conservatives on this issue."

He goes further: "I don't believe the Lib Dems can look the electorate in the eye if they go back on their word. We would be happy to work with them on an alternative way of funding higher education." As for the Conservatives, he talks of a "constructive" relationship with Willetts in opposition. "He surprised us, a Tory minister, and I hope we surprised him as a national union."

Indeed, the politician has been full of praise for the NUS. When in opposition Willetts said the transformation of the union and its new way of fighting was "the most powerful single way of making sure that politicians listen". That was in October 2009, at an NUS conference. It was there that Willetts claimed the case for raising the cap had not been won by universities. "How would I vote today? I think I would say today, if the vote arose, that the case has not been made," he said. "This is not an argument that I believe the universities have won. They haven't yet properly accounted for the first £3,000 they had, so I would say not unless, and until, you have shown what is in it for students and their parents."

Porter hopes to convince Willetts that vice-chancellors have still not won the argument. "I don't think universities have made the case sufficiently about how they could improve what students receive," he says, saying the call for higher fees lacks "legitimacy".

Porter believes that failure by the NUS to win this argument will hurt those from the poorest backgrounds in the long run, who are deterred from applying to university. Those that do choose to study at a higher level may have to stay at home missing out on the extracurricular activities such as volunteering and clubs – not to mention learning to live independently, "to cook and wash for themselves".

Then there is the post-university impact. Heavy fees could mean different decisions about marriage, he argues, and could create a society in which graduates habitually rent instead of buying homes. "I recognise the pressures on university and college funding but they have had a decade of almost exponential investment and very few of them had the foresight to realise there might be a few years of difficulties." His argument is that it is not fair to burden students with the cost of that failure.

Porter perhaps owes his own political drive to his mother, who timed dinner with the six o'clock news when he was growing up. "I remember taking an unhealthy interest in the 1992 election," he says. "I was seven."

Should he fail and fees go up, he says: "I don't think vice-chancellors are so bloodthirsty that they would not make some grants available. But if you graduate with £50,000 of debt, or £80,000 or £90,000 if you are a medic... I would think twice." As for the struggle, it will be a bit of the old and a bit of the new, he says: meetings behind closed doors with the likes of Willetts, Cable and Browne – but an old-fashioned national demonstration to remind the country that students still know how to shout.